The present invention relates to optical imagesplitting apparatus.
U.S. Pat. No. 3,652,167 in the name of Francis Hughes Smith describes an optical apparatus for measuring the lateral dimensions of objects by the procedure of image splitting, wherein the required dimension is obtained by adjusting the relative lateral displacement between two identical images of the object until the latter's relevant edges appear only just in contact.
However, experience has shown that the form of optical image-shearing systems described in the aforementioned specification presents substantial manufacturing difficulties. For example, the separate mirrors for the respective split images need separately adjusting to inconveniently precise limits and the orientations of the quarter-wave plates in front of the respective mirrors require careful adjustment to ensure that the split images have similar intensity.